Postfix does allow you to add logging messages for subject lines, and so we’ll use this to simply log a warning message for any subject line. It’s a bit of a ‘hack’, but works and doesn’t cause any problems (Postfix doesn’t block or alter the emails).

” INDEX
Indicates an index (position) within the current FILE. The position is specified in mm:ss:ff (minute-second-frame) format. There are 75 such frames per second of audio. In the context of cue sheets, “frames” refer to CD sectors, despite a different, lower-level structure in CDs also being known as frames.[5] INDEX 01 is required and denotes the start of the track, while INDEX 00 is optional and denotes the pregap. The pregap of Track 1 is used for Hidden Track One Audio (HTOA). Optional higher-numbered indexes (02 through 99) are also allowed.
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